The invention relates to a device for the separation of a fluid into at least two fractions.
The invention is used in particular for the separation of paint and solvent, in containers of paint or of rinsing water recovered from motor vehicle bodies, in an installation for painting by cataphoresis.
Numerous fluids and in particular numerous liquids used under industrial conditions require separation operations, for example in order to be regenerated and recycled in an industrial process in which they are used.
In certain cases, one of the fractions separated from the fluid is eliminated, the other fraction being reused and, in other cases, the two fractions obtained by the separation are reused.
For example, in the case of installations for painting by electrophoresis or cataphoresis of motor vehicle bodies, this operation generally being aimed at producing an anti-corrosion base coat on the body, the separation operations can be carried out on a paint bath in which the bodies are immersed or on the water recovered after rinsing the body. In both cases, a first fraction is recovered, constituted by the paint solvent, i.e. in general a mixture of demineralized water and organic solvents which can also contain salts and other substances. This first fraction can be reused for rinsing the bodies. A second recovered fraction which is constituted by the paint can be recycled into the container containing the paint bath.
In other applications, in the field of the motor industry and more generally in the mechanical or surface treatment industries, the separation of substances contained in synthetic oils or water used for rinsing industrial articles can be carried out after degreasing, phosphatization and painting or also the recovery of paint which can be diluted in water.
In the field of the environmental conservation, it can also be necessary to carry out separation operations, for example for the treatment of cutting oils, biodegradable effluents or non-biodegradable effluents.
The separation devices used industrially generally comprise a membrane filter with which the fluid on which the separation operation is to be carried out is brought into contact, in such a manner that at least a part of the fluid passes through the membrane filter.
Filtration can be carried out by causing first fraction of the fluid to pass through the membrane, a second fraction contained in the fluid in homogeneous or non-homogeneous form being stopped by the membrane filter the pores of which allow the first fraction of the fluid to pass through.
A usual filtration process in which the fluid is passed through the membrane by gravity or by a pressure difference has the drawback of bringing about a rapid clogging of the membrane filter, due to the fact that the particles in the fraction of the fluid retained by the membrane are coated against the surface of the membrane and have a tendency to become fixed on the surface of the membrane or in the pores through the membrane.
It is very often preferable to resort to a process of separation with tangential circulation of the fluid in contact with the membrane, such as ultrafiltration utilizing a membrane the pores of which have a nanometric dimension. In order to carry out the separation, the fluid is circulated in contact with a surface of the membrane in a tangential direction. The fluid thus produces a continuous sweeping of the membrane, such that the particles which cannot pass through the ultrafiltration membrane of are entrained by the fluid and do not therefore have a tendency to accumulate on the surface of the ultrafiltration membrane.
On either side of the membrane a pressure difference is created, which can be of the order of a few bars which ensures the passage of a fraction of the fluid through the pores of the membrane, this fraction of the fluid being called the permeate.
The other fraction of the fluid, called the retentate, which cannot pass through the ultrafiltration membrane through the pores of this membrane circulates in contact with the surface of the ultrafiltration membrane in a tangential direction in order to be recovered in the vicinity of one end of the membrane.
In the case of the separation of solvent and paint, the solvent constitutes the permeate and the paint, the retentate.
Ultrafiltration separation devices are known which are constituted by modules in which the ultrafiltration membranes are coiled on themselves with insertion of a grid between the successive coils of the membrane. In such modules, called spiral modules, the circulating fluid is slowed down by the spacing grid and moreover, the particles which can be transported by the retentate are capable of clogging the grids.
Ultrafiltration fluid separation modules have been proposed in which the fluid and the retentate, circulating in a tangential manner relative to the ultrafiltration membrane, are not slowed down by any element inserted between the membranes.
Such ultrafiltration separation modules can in particular comprise plane membrane-support plates having two opposite faces on each of which an ultrafiltration membrane is fixed. Generally, the ultrafiltration membrane is mounted on part of the surface of the membrane-support plate comprising the fluid-guiding means, for example ribs delimiting between them grooves for the drainage of the permeate passing through the ultrafiltration membrane towards evacuation channels which can be provided in a lateral part of the membrane-support plate and the obtaining of turbulence in the outflow of the fluid. Each of the membranes delimits, with the part of the membrane-support plate on which it is mounted and fixed, a permeate recovery space in which the permeate is entrained towards the evacuation channels, inside the grooves.
The membrane-support plates constituting an ultrafiltration module are mounted one against the other with the insertion of a seal between the peripheral parts of two successive plates. The seal ensures that a fluid reception and circulating space is tightly sealed towards the outside of the module, the fluid reception space being delimited inside the module, by two ultrafiltration membranes facing one another and fixed on two opposite faces of two adjacent membrane-support plates.
The peripheral seals inserted between two successive membrane-support plates also ensure the maintenance of a gap between the membrane-support plates and between the opposite membranes which is necessary to ensure the passage of the fluid to be filtered in circulation between the two opposite membranes, inside the reception and circulation space. Means for supplying the fluid reception and circulation spaces are provided at one of the ends of the membrane-support plates and of means for recovering the retentate are provided at the opposite ends of the membrane-support plates. During the circulation of the fluid in the reception and circulation spaces between the membranes, the first fraction of the fluid constituting the permeate passes through the membranes, on both sides of reception and circulation space, in order to penetrate into the permeate recovery spaces delimited by each of the membranes. The fluid circulating in the reception and circulation spaces separated from the first fraction constituting the permeate, for example, a solvent in the case of a mixture of solvent and paint, constitutes the retentate which is constituted for example by the paint in the case envisaged above.
The permeate penetrating into the recovery spaces is drained by the grooves of the membrane-support plates in order to reach means of recovery connected with means of evacuation of the permeate which are connected to the ultrafiltration module.
At its ends, i.e. at the level of the first and last plate in the stack of the module, the latter is closed by rigid plates or retaining means which are mounted against the first and the last plates of the module with the insertion of a seal. The supply of fluid on which separation and recovery of the permeate and retentate is carried out can be achieved at the level of the retaining means.
Tie rods ensure the assembly of the membrane-support plates, being clamped one against the other by means of the seals, between the two retaining means.
Moreover, a separation device or module can comprise several successive sub-assemblies separated from each other by separating plates, the different successive modules being inserted between two retaining plates at the ends of the device.
Inside a sub-assembly of a module, between two separating plates or between a retaining plate and a separating plate, the fluid is distributed in the different successive reception and circulation spaces and the retentate is recovered at the outlet of the circulation spaces then collected at the outlet of the sub-assembly in order to be optionally introduced into a following sub-assembly. The retentate is distributed in the circulation spaces and constitutes the fluid on which the separation is carried out in the second sub-assembly. In other words, the different circulation spaces of a sub-assembly are mounted in parallel and the successive sub-assemblies of a module are mounted in series.
The successive membrane-support plates of the sub-assemblies and the successive sub-assemblies of a module are assembled in juxtaposed position with insertion of tightness seals, using tie rods the clamping of which is ensured at the level of the retaining plates. Each of the tie rods passes through a peripheral part of each of the membrane-support plates, separating plates and retaining plates.
The permeate is drained into each of the permeate-recovery spaces delimited between a membrane and a face of a membrane-support plate, towards recovery means connected to channels for evacuation of the permeate which can be connected to pumping means outside the filtration module.
The permeate-evacuation channels can be formed by openings passing through the membrane-support plates, the separating plates and at least one of the retaining plates which are placed in the alignment with one another, during the assembly of the module. This compact arrangement has advantages but, however, the circulation of the permeate which is carried out entirely inside the module cannot be made visible from the outside of the module, with the result that visual checking of the functions of the different elements constituting the module cannot be carried out. In particular, when a colouration or a turbidity of the permeate is detected at the module outlet due to the fact that at least one membrane has a leak, no simple means are available for determining the position of the membrane having a leak and for interrupting the circulation of fluid in the permeate recovery space delimited by the membrane having a leak. Moreover, the colouration or the turbidity of the permeate at the module outlet, due to the dilution of the permeate originating from the different elements of the module, is apparent only when the leak flow rate through the defective membrane has become very significant.
Damage to the membranes leading to the appearance of a leak can to a large extent be limited or avoided by taking measures to avoid elements capable of damaging the membranes being able to come into contact with them. For example, in order to avoid solid particles of prohibited dimensions capable of tearing the ultrafiltration membranes coming into contact with the ultrafiltration membranes, a pre-filtration of the fluid can be carried out before its introduction into the ultrafiltration module. Precautions can also be taken as regards the conditions of use of the ultrafiltration installation, for example as regards the stopping and starting operations of the installation.
However, there is a not-insignificant risk of damaging membranes during the operation of the separation device.
Certain types of ultrafiltration module make it possible to carry out control of the operation of the different elements of the module and in particular leak control of the membranes of the module. In these installations, each of the permeate-recovery spaces is linked to one or more collectors arranged outside the module, by means of transparent flexible pipes which allow the outflow of permeate originating from each of the recovery spaces to be made visible.
When a certain colouration or a certain opacity of the permeate appears inside a flexible pipe connecting a permeate recovery space to a collector, the two ends of the connecting pipe are disconnected, at the ultrafiltration module and at the collector and the module outlet and the collector inlet are plugged with stoppers.
It is also possible to connect the end of the connecting pipe outside the module to a leak-recovery collector.
In all cases, the plugging operation or operation for connecting to a leak collector require the removal of a connecting pipe, which results in an ejection of permeate in the locality where the installation is situated and possibly bringing the operators responsible for the plugging operation or operation for connecting to the leak connecter, into contact with the permeate, which can be unpleasant or even dangerous, depending on the nature of the fluid treated.
Moreover, there is a risk that the flexible connecting pipes which are outside the module will become caught and damaged by operators or handling equipment moving in the vicinity of the module.